The present invention relates to a signal conducting wires or conductors, particularly to those used by the telephone industry.
Present day telephone distribution is accomplished between a central office and local subscribers by main distribution or feeder cables branching out into individual trunk and local lines. Above ground distribution for residential service utilizes pole supported cables feeding terminals from which drop wires continue the connection to the various buildings being served. The present invention provides a new drop wire and a new approach to drop wire installation.
The drop wire has traditionally consisted of a single conductive pair suitably insulated and strengthened to be weatherproof and to withstand the stresses encountered in runs of up to 200 ft. from pole to building. Generally where residential service is involved, a separate single pair drop wire is installed using separate installation hardware for each phone line requested by the customer. It should be evident that this practice, particularly if the lines are not ordered at the same time, entails doubling up on expense both for parts and labor.
There was a time when the standard drop wire consisted of two conductors, rubber insulated, and covered with neoprene. More recently, an all PVC insulated drop wire was developed and received some acceptance by the industry. Also accepted by the industry is a wire construction developed by the assignee of the present invention. Known as "Alpha-Tel" drop wire, it contains a pair of 181/2 AWG (0.0385"), 30% conductivity copper clad steel wire conductors. The insulation-jacket on such wire has been formulated of ethylene/propylene rubber (EPR).
The configuration is generally flat with overall cross-sectional dimensions of about 0.135".times.0.220". The breaking strength of such wire is about 230 pounds.
In the past attempts were made by others to produce plastic insulated drop wire constructions having performance capability comparable to that of the rubber insulated variety. Thus, there is described in Taylor U.S. Pat. No. 2,950,338, issued Aug. 23, 1960 for "Plastic Insulated Electrical Line and Mounting Therefor," "a drop-wire having at least one wire conductor of a size in cross-section determined by the current carrying capacity required thereof and a support or strength member, as for example a steel wire, of substantially larger diameter than the conductor, both the conductor and support member being embedded in spaced parallel relation to each other in a thermoplastic insulation, such as polyethylene; together with a clamp which is adapted and arranged to bite through the insulation of the wire in a direction substantially perpendicular to the plane defined by the support member and conductor, whereby the jaws of said clamp are brought into direct frictional engagement with the support member but are prevented from coming into contact with the conductor by such engagement with the support member. The clamp, thus firmly gripping the drop-wire, is then fastened to the pole or building, as the case may be, so that the weight of the span of drop-wire is carried by the clamp which, being in rigid engagement with the support member in the wire, transmits all the tensile forces to that member instead of to the jacket or conductors of the drop-wire." A specific embodiment is described in the patent as comprising a 1/16" diameter galvanized steel wire that functions as a central support member having a tensile strength on the order of 135,000 p.s.i. The embodiment is stated as being capable of meeting the alleged minimum 400 pound tensile load requirements for standard telephone drop-wire. In addition, two bare soft copper conductors of No. 22 AWG wire are located parallel to and on opposite sides of the support member. The three wires are embedded in polyethylene insulation.
One of the advantages specifically ascribed by Taylor to his drop wire is that in installations where an electrical ground is not readily available the support member in the drop wire may be used as the ground. In that event the support wire was to be connected to a suitable ground at the telephone pole. It was of the essence in the Taylor concept, as asserted in his patent, that the support member be of larger diameter than the conductors and that the conductors be positioned such that the jaws of the mounting clamp could be forced through the insulation into direct contact with the support member without engaging the conductors.
Drop wires in current use are generally of flat construction and are engaged by a wedge type clamp for fastening to poles, trees, buildings and other supporting structure. Such clamps are known as "P" clamps.